#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <string>

#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <ctype.h>
using namespace std;
const int basesize = 1024;
const int argvnum = 64;
const int envnum = 64;
// 全局的命令⾏参数表
char *gargv[argvnum];
int gargc = 0;
// 全局的变量
int lastcode = 0;
// 我的系统的环境变量
char *genv[envnum];
// 全局的当前shell⼯作路径
char pwd[basesize];
char pwdenv[basesize];
// " "file.txt
#define TrimSpace(pos) do{\
while(isspace(*pos)){\
pos++;\
}\
}while(0)
string GetUserName()
{
string name = getenv("USER");
return name.empty() ? "None" : name;
}
string GetHostName()
{
string hostname = getenv("HOSTNAME");
return hostname.empty() ? "None" : hostname;
}
string GetPwd()
{
if(nullptr == getcwd(pwd, sizeof(pwd))) return "None";
snprintf(pwdenv, sizeof(pwdenv),"PWD=%s", pwd);
putenv(pwdenv); // PWD=XXX
return pwd;
//string pwd = getenv("PWD");
//return pwd.empty() ? "None" : pwd;
}
string LastDir()
{
string curr = GetPwd();
if(curr == "/" || curr == "None") return curr;
// /home/whb/XXX
size_t pos = curr.rfind("/");
if(pos == std::string::npos) return curr;
return curr.substr(pos+1);
}
string MakeCommandLine()
{
// [whb@bite-alicloud myshell]$
char command_line[basesize];
snprintf(command_line, basesize, "[%s@%s %s]# ",\
GetUserName().c_str(), GetHostName().c_str(), LastDir().c_str());
return command_line;
}
void PrintCommandLine() // 1. 命令⾏提⽰符
{
printf("%s", MakeCommandLine().c_str());
fflush(stdout);
}
bool GetCommandLine(char command_buffer[], int size) // 2. 获取⽤⼾命令
{
// 我们认为：我们要将⽤⼾输⼊的命令⾏，当做⼀个完整的字符串
// "ls -a -l -n"
char *result = fgets(command_buffer, size, stdin);
if(!result)
{
return false;
}
command_buffer[strlen(command_buffer)-1] = 0;
if(strlen(command_buffer) == 0) return false;
return true;
}
void ParseCommandLine(char command_buffer[], int len) // 3. 分析命令
{
(void)len;
memset(gargv, 0, sizeof(gargv));
gargc = 0;
// "ls -a -l -n"
const char *sep = " ";
gargv[gargc++] = strtok(command_buffer, sep);
// =是刻意写的
while((bool)(gargv[gargc++] = strtok(nullptr, sep)));
gargc--;
}
void debug()
{
printf("argc: %d\n", gargc);
for(int i = 0; gargv[i]; i++)
{
printf("argv[%d]: %s\n", i, gargv[i]);
}
}
// 在shell中
// 有些命令，必须由⼦进程来执⾏
// 有些命令，不能由⼦进程执⾏，要由shell⾃⼰执⾏ --- 内建命令 built command
bool ExecuteCommand() // 4. 执⾏命令
{
// 让⼦进程进⾏执⾏
pid_t id = fork();
if(id < 0) return false;
if(id == 0)
{
//⼦进程
// 1. 执⾏命令
execvpe(gargv[0], gargv, genv);
// 2. 退出
exit(1);
}
int status = 0;
pid_t rid = waitpid(id, &status, 0);
if(rid > 0)
{
if(WIFEXITED(status))
{
lastcode = WEXITSTATUS(status);
}
else
{

lastcode = 100;
}
return true;
}
return false;
}
void AddEnv(const char *item)
{
int index = 0;
while(genv[index])
{
index++;
}
genv[index] = (char*)malloc(strlen(item)+1);
strncpy(genv[index], item, strlen(item)+1);
genv[++index] = nullptr;
}
// shell⾃⼰执⾏命令，本质是shell调⽤⾃⼰的函数
bool CheckAndExecBuiltCommand()
{
if(strcmp(gargv[0], "cd") == 0)
{
// 内建命令
if(gargc == 2)
{
chdir(gargv[1]);
lastcode = 0;
}
else
{
lastcode = 1;
}
return true;
}
else if(strcmp(gargv[0], "export") == 0)
{
// export也是内建命令
if(gargc == 2)
{
AddEnv(gargv[1]);
lastcode = 0;
}
else
{
lastcode = 2;
}
return true;
}
else if(strcmp(gargv[0], "env") == 0)
{
for(int i = 0; genv[i]; i++)
{
printf("%s\n", genv[i]);
}
lastcode = 0;
return true;
}
else if(strcmp(gargv[0], "echo") == 0)
{
if(gargc == 2)
{
// echo $?
// echo $PATH
// echo hello
if(gargv[1][0] == '$')
{
if(gargv[1][1] == '?')
{
printf("%d\n", lastcode);
lastcode = 0;
}
}
else
{
printf("%s\n", gargv[1]);
lastcode = 0;
}
}
else
{
lastcode = 3;
}
return true;
}
return false;
}
// 作为⼀个shell，获取环境变量应该从系统的配置来
// 我们今天就直接从⽗shell中获取环境变量
void InitEnv()
{
extern char **environ;
int index = 0;
while(environ[index])
{
genv[index] = (char*)malloc(strlen(environ[index])+1);
strncpy(genv[index], environ[index], strlen(environ[index])+1);
index++;
}
genv[index] = nullptr;
}
int main()
{
InitEnv();
char command_buffer[basesize];
while(true)
{
PrintCommandLine(); // 1. 命令⾏提⽰符
// command_buffer -> output
if( !GetCommandLine(command_buffer, basesize) ) // 2. 获取⽤⼾命令
{
continue;
}
//printf("%s\n", command_buffer);
ParseCommandLine(command_buffer, strlen(command_buffer)); // 3. 分析命令
if ( CheckAndExecBuiltCommand() )
{
continue;
}
ExecuteCommand(); // 4. 执⾏命令
}
return 0;
}







